If the counterargument to knowledge graph-based memory systems is that they're slow and take multiple steps, then it's not really a counterargument. I'd happily trade off speed for giving the agent ability to find more precise memories.

That said, I think this article's basic idea of "text files + semantic search index" is a good way to implement memory because AI is already good at search, and semantic search is far more flexible than a knowledge graph and decreases the chance of the agent simply not being able to find a memory (or inserting duplicate memories, etc.) due to deciding to go into a slightly different branch than the one it needed to travel.

That said, I'd probably layer additional steps on top for further efficiency improvements. For example, automatic concise summaries of memory items, other supplemental indexing methods for better memory recall, etc. My ideal solution would be multi-step and therefore wouldn't solve the knowledge-graph's slowness, but it would solve the rigidness problem of a knowledge graph.